Is my newly acquired Alesis Recital Pro digital piano keyboard out of tune or is my musical acumen failing with age?
First some facts. The Recital Pro is an 88 key keyboard so spans from lower A0 to upper C8 with an overall pitch range of just over 7 octaves. It boasts 12 basic voices with various additional functions. Some of the voices (namely "Clavi", "Acoustic bass" and "Fingered bass") sound an octave lower than normal giving effectively an overall range of just over 8 octaves, although this shift is tacitly cancelled when layering with a normal voice. Moreover the whole range can be "transposed" by up to 12 semitones up or down extending the effective range to about 10 octave but q.v..
In what follows the term "normal" will refer to the standard piano pitches with A4 (above middle C) having the frequency 440Hz (this being Concert Pitch by definition).
The keyboard extends downwards 4 octaves and upwards 3 and a bit octaves from A4 so we have:
C8 ~4186Hz (highest normal note, all C frequencies per equal temperament)
A7 3520Hz
A6 1760Hz
A5 880Hz
A4 440Hz (standard pitch)
C3 ~261.6Hz (middle C, 2ft open pipe e.g. flute)
A3 220Hz
A2 110Hz
A1 55Hz
C1 ~32.7Hz (16ft open pipe)
A0 27.5Hz (lowest normal note)
With voice "Fingered bass" selected the lowest note becomes C0 at 16.35Hz and the A below at 13.75Hz, and with decent headphones on (because the internal speakers have poor low frequency response) the sound is impressive and reminiscent of a real (acoustic) organ at 32ft register. The sound is a combination of deep bass and tangible throbbing (at 13.75 times per second). Of course, the listener is probably hearing the harmonics (or "partials") rather more than the fundamental, witness with the purer voice "Acoustic bass" for which the deep bass is hardly audible, but this fact hardly detracts from the experience because non-linearities themselves can create undertones giving the illusion of bass deeper than the equipment should be able to produce.
But one can go even lower in pitch with "Transpose" set to its minimum of "-12" i.e. 12 semitones lower. With this setting the lowest note to sound is C#0 which calculates as 8.66Hz and sounds little more than a throbbing, and this simulates the 64ft organ open pipe register.
Similarly with "Transpose" set to positive amounts one can explore the Recital Pro's upper register. In principle, by playing the top note, with the settings up to the maximum of "+12" one should get up to B8 at 7902.13Hz. In fact with the standard "Piano" voice there is already hardly any output at top C even without any transposing (as indeed with an acoustic piano). Apart from obviously the voices that sound an octave below normal, the voice "Synth" perhaps does the best at top C. Then, as the "Transpose" setting is increased up to "+12" sampling alias artefacts become very evident and at "+12" the apparent pitch seems actually lower than with setting "00". Which suggests that, internally, the digital pitch engine is sampling maybe lower than the industry standard 44.1kHz or at least there is insufficient anti-aliasing filtering. All this is a bit academic because I have no call to be making noises at this high a frequency. But maybe younger players with better hearing might want to.
Both effortless low frequency response and high frequency response plagued with aliasing are of course typical of any digital audio system.
But back to my opening gambit. I play mostly by ear so hit notes that my "ear" thinks are correct, rather than reading them from a music score. I have found with my Recital Pro that I not infrequently find myself playing notes in the lower register that are entirely incorrect and yet taking a while to notice it. Which I cannot remember doing on an acoustic piano. Or I find, even when the score confirms I am playing the correct note, it just doesn't sound right.
Now, as I've said this may be due to my ailing musical acumen or else it could be a real effect and I'd be interested to hear if my readers have any similar experiences or observations. If it is a real effect then I suspect it is related to the Railsback effect observed in acoustic pianos and thus possibly simulated in their digital counterparts.
The deal here is that real (acoustic) piano strings have thickness as well as length. Based on length alone (and thus assuming no effect of bending at either end), a string can vibrate with fundamental and harmonics. By definition the frequencies of the harmonics are integer multiples of that of the fundamental. But if the resistance to bending near the fulcrums is taken into account what were harmonics become mere overtones i.e. no longer having exact integer relationship with the fundamental indeed becoming "inharmonic". In a piano the lower pitch strings have to be made heavier than mere scale would demand in order that their length and thus the overall dimensions of the instrument should remain feasible for the average owner. Not only that but the lower the pitch, then more the "ear" is aware of the overtones over and above the fundamental because of the tail-off of low frequency response of the ear and of the piano's sounding board. To compensate the piano tuner favours the first few overtones over and above the fundamental and thus has to effectively detune the lower strings.
A similar effect applies to the higher strings where it becomes necessary for mechanical robustness to make the strings thicker than mere scale would demand, thus increasing inharmonicity.
The overall effect is the Railsback curve which sort of averages, I suppose, what piano tuners have been trained to do as part of their art. Which of course applies to acoustic pianos and contributes to their overall sound quality.
Enter the digital piano. Of course, when tuned, there is now no reason to copy the Railsback curve as far as mechanics are concerned as there are none. But what does persist is the piano players' expectations, and the article linked above suggests that digital pianos do regard Railsback and perhaps that is why the lower register of my Recital Pro sometimes seems over of tune to my ears.
Comments please!
